1. Field of the Invention
The invention relates to an injection molding method and apparatus, and more particularly to a method and apparatus for manufacturing metallic parts by injection molding using a separate ingot melt furnace and feeder.
2. Description of the Related Art
Injection molding is a known method used to produce molded metallic parts from melted metal. A conventional injection molding apparatus 1 is illustrated in FIG. 1. In an injection molding method using apparatus 1, metal ingots or particles 3 are supplied directly to a melt feeder or hopper 5 in the solid state. The ingots 3 settle to the bottom of the melt feeder 5, and rest on a filter 7, such as a grate, while they are melted by heaters 9. The melted metal 11 is then released into an injection chamber 13. The melt feeder 5 contains a pipe 15 which supplies an inert protective gas, such as argon or nitrogen, to the melt feeder to drive out any air which may have become trapped in the molten metal 11, as described for example in U.S. Pat. No. 5,501,266, incorporated herein by reference in its entirety. The molten metal 11 is then injected into a mold cavity 17 by a piston or plunger 19. The piston may have a shape of a rod or a screw extending throughout the length of the injection chamber 13, past the opening to the feeder 5, as described in U.S. Pat. No. 5,501,266. The metal 11 solidifies in the mold cavity 17 to form the molded metallic part. However, this prior art method and apparatus suffer from several disadvantages.
The melt feeder 5 must contain a certain minimum volume of the molten metal 11 in order to allow a continuous, uninterrupted operation of the injection molding apparatus 1. Thus, the melt feeder 5 must have a minimum height in order to hold at least the minimum volume of the molten metal 11. For example, the melt feeder 5 should have a height of about four feet in order to ensure the uninterrupted operation of the apparatus 1.
A delivery system, such as a conveyor 21 or a downwardly sloped surface, which delivers the ingots or pellets 3 to the melt feeder 5 is located above the melt feeder, as illustrated in FIG. 1. The ingots 3 are dropped into the melt feeder 5 by the delivery system 21 from a relatively large height, such as 4-5 feet. The drop causes the ingots 3 to create a splash on contact with the molten metal 11 present in the melt feeder 5. The splashed molten metal hits the upper portions of the metal feeder 5 and the pipe 15 and solidifies as plaque 23, because the upper portions of the melt feeder 5 and the pipe 15 are maintained at a lower temperature than the lower portions of the melt feeder for safety reasons. This is particularly true for a metal such as magnesium which can easily catch fire when it contacts air surrounded by a wall of a higher temperature.
The plaque 23 blocks the egress from the pipe 15, interfering with the delivery of the protective inert gas and forms thick deposits on the walls of the melt feeder 5, which requires expensive and time consuming maintenance to remove these deposits. The apparatus 1 has to be taken off line during maintenance, further increasing manufacturing expenses. The present invention is directed at overcoming or at least reducing these and other problems of the prior art.
In one aspect of the present invention, there is provided a method of forming a molded object, comprising introducing solid material into a first chamber, melting the solid material in the first chamber, transferring the melted material from the first chamber into a second chamber, transferring the melted material from the second chamber into a third chamber, transferring the melted material from the third chamber into a mold cavity, and solidifying the melted material in the mold cavity to form the molded object.
In another aspect of the present invention, there is provided an injection molding apparatus, comprising a first chamber means for melting a solid material, a second chamber means for holding the melted material, a third chamber means for holding the melted material to be transferred into a mold cavity, a first conduit means for transferring the melted material from the first chamber means to the second chamber means, a second conduit means for transferring the melted material from the second chamber means to the third chamber means, and a first piston means in the third chamber means for transferring the melted material from the third chamber means to a mold cavity.
In another aspect of the present invention, there is provided an injection molding apparatus, comprising a melt furnace suitable for melting a metal, a feeder suitable for holding the melted metal, an injection chamber containing a first piston and an injection nozzle, a first conduit connecting the melt furnace to the feeder, and a second conduit connecting the feeder to the injection chamber.
In another aspect of the present invention, there is provided an injection molding apparatus, comprising a melt furnace suitable for melting a metal, a screening element adjacent to a bottom of the melt furnace comprising at least one non-horizontal wall, a top and a melt furnace outlet on at least one wall, an injection chamber containing a piston and an injection nozzle, and a conduit connecting the melt furnace outlet to the injection chamber.